1. Field of Invention
The present invention relates to a touch screen and a flat panel display (FPD), and more particularly, to a touch screen FPD.
2. Related Art
Currently, capacitive touch screens are classified into digital capacitive touch screens and analog capacitive touch screens. The digital capacitive touch screen is composed of two layers of electrodes each having a plurality of parallel electrodes, and the two layers of electrodes are orthogonal to each other. A touch excitation signal is applied to each electrode, and when a finger of a human touches the touch screen, the finger forms a coupling capacitor with some electrodes on the touch screen, and a leakage current flows from the coupling capacitor. The touch system circuit determines two orthogonal electrodes forming the coupling capacitor with the finger on the two layers of electrodes through detecting the leakage current, thus determining the position of the touch. However, this method is only adapted to rough positioning, and when it intends to perform fine positioning, two layers of fine and close electrodes are required, which, however, has a high cost. Moreover, when the digital capacitive touch screen is disposed in front of the display, reflection generated by sensing lines causes a nonuniform display.
The analog capacitive touch screen can be classified into tow types, namely, the analog capacitive touch screen having a single layer of sensing line and having two layers of sensing lines. The analog capacitive touch screen having a single layer of sensing line inputs touch excitation current signals to the electrode from four corners of the single-layered electrode, and when a finger of a human touches the touch screen, a coupling capacitor is formed by the finger and the electrode, and a leakage current flows from the coupling capacitor. The touch system circuit determines through calculation the touch position where the current flows from the finger through detecting magnitudes of the current respectively flowing from the four corners to the electrode. This method can realize the fine positioning, however, the control circuit requires a large calculation amount, and when the ambient temperature and humidity change so as to change the ambient electric field, drift occurs, thus causing inaccurate positioning. When the touch screen is disposed in front of the display, inadequate transmission of the sensing lines of the touch screen reduces the brightness of the display screen, and reflection generated by the sensing lines of the touch screen further reduces the display contrast under strong ambient light.
The analog capacitive touch screen having two layers of sensing lines is composed of two layers of electrodes each having a plurality of parallel electrodes, and the two layers of electrodes are orthogonal to each other. A touch excitation signal is applied to each electrode, and when a finger of a human touches the touch screen, the finger forms a coupling capacitor with some electrodes on the touch screen, and a leakage current flows from the coupling capacitor. The touch system circuit obtains through calculation touch positions in horizontal or longitudinal direction respectively on the two layers of electrodes orthogonal to each other by detecting magnitude of the current flowing from each electrode. This method can realize the fine positioning, and also alleviate the drift problem. However, the two layers of sensing lines must be detected one by one for detecting the leakage current, so a large detection and calculation amount is required, and time spent for detection and calculation is also increased along with the increase of the size of the screen and the increase of the sensing lines. When the touch screen is disposed in front from the display, reflection generated by the sensing lines of the touch screen results in a non-uniform display, as well as a reduced display contrast under strong ambient light.
Patent No. CN1678980 entitled “Touch Sensing” has disclosed a method using electrodes of a matrix FPD as touch sensors, such that the FPD has the function of sensing touch. However, in this method, electrodes of the FPD have introduction ends disposed at one side to be connected to a display driving circuit and have introduction ends disposed at the opposite side to be connected to a touch system circuit, such that the electrodes of the display communicate with the display driving circuit or the touch system circuit at different times, and the electrodes of the display serve as sensing lines to sense the touch. The method of introducing leads from two ends of the column electrodes and the row electrodes to be respectively connected to the display driving circuit and the touch system circuit greatly increases the density and complexity of the introduction leads, thus increasing the cost and reducing the reliability.
Patent application No. 2006100948141 entitled “Touch Screen Flat Panel Display” has disclosed a connection mode between a touch system circuit and electrodes of a display screen, in which an analog switch is used to enable the electrodes of the display screen to transmit display driving signals, or transmit and sense touch signals, such that display driving and touch detection time-division multiplex the electrodes of the display screen, and the electrodes of the display screen are used for display driving as well as touch detection. Patent application No. 2006101065583 entitled “Planar Display Device with Touch Controllable Function” has disclosed another connection mode between a touch system circuit and electrodes of a display screen, in which a signal loading and merge circuit enables the electrodes of the display screen to transmit display driving signals and transmit and sense touch signals simultaneously, such that display driving and touch detection share the electrodes of the display screen simultaneously, and the electrodes of the display screen are used for display driving as well as touch detection. The disclosed modes make the connection of the touch system circuit and the electrodes of the display screen reasonable, and even skillfully utilize selection and output circuit parts in the display driving circuit, such that the connection between the touch system circuit and the electrodes of the display screen becomes simple and feasible.
In the above patents, a touch excitation signal is applied to electrodes of the display screen one by one in a scan addressing mode, so as to detect touch on the electrodes one by one in the row direction and the column direction. Row and column electrodes of the flat panel display screen are intersected to form a mesh-like structure, and the touch excitation signal applied to one electrode series-flows among the mesh-like electrodes of the flat panel display screen, thus influencing the determination to the touched electrodes.